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Prolonged isolation and persistence of a common endemic on granite outcrops in both mesic and semi-arid environments in south-western Australia

Authors

  • Sarah-Louise Tapper,

    1. Science and Conservation Division, Department of Parks and Wildlife, Perth, WA, Australia
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  • Margaret Byrne,

    Corresponding author
    1. Science and Conservation Division, Department of Parks and Wildlife, Perth, WA, Australia
    • Correspondence: Margaret Byrne, Science and Conservation Division, Department of Parks and Wildlife, Locked Bag 104, Bentley Delivery Centre, WA 6983, Australia.

      E-mail: Margaret.Byrne@dpaw.wa.gov.au

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  • Colin J. Yates,

    1. Science and Conservation Division, Department of Parks and Wildlife, Perth, WA, Australia
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  • Gunnar Keppel,

    1. Curtin Institute for Biodiversity and Climate, and School of Science, Curtin University, Perth, WA, Australia
    2. School of Natural and Built Environments and Barbara Hardy Institute, University of South Australia, Adelaide, SA, Australia
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  • Stephen D. Hopper,

    1. Centre of Excellence in Natural Resource Management, and School of Plant Biology, The University of Western Australia, Albany, WA, Australia
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  • Kimberly Van Niel,

    1. School of Plant Biology, The University of Western Australia, Perth, WA, Australia
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  • Antonius G. T. Schut,

    1. Curtin Institute for Biodiversity and Climate, and School of Science, Curtin University, Perth, WA, Australia
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  • Laco Mucina,

    1. Curtin Institute for Biodiversity and Climate, and School of Science, Curtin University, Perth, WA, Australia
    2. School of Plant Biology, The University of Western Australia, Perth, WA, Australia
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  • Grant W. Wardell-Johnson

    1. Curtin Institute for Biodiversity and Climate, and School of Science, Curtin University, Perth, WA, Australia
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Abstract

Aim

Granite outcrops may be able to act as refugia for species during adverse climate change, owing to their topographic complexity. We assessed this hypothesis by examining phylogeographical patterns in a common, geographically widespread granite endemic, Stypandra glauca (Hemerocallidaceae).

Location

Granite outcrops of the Southwest Australian Floristic Region, Western Australia.

Methods

Twenty-four tetraploid individuals of the granite endemic Stypandra glauca were sampled from each of 12 granite outcrops: 7 from a mesic environment and 5 from the semi-arid region. Phylogenetic reconstruction and divergence-dating was achieved using Bayesian and parsimony analyses of chloroplast haplotypes from 90 individuals. Nuclear diversity and population differentiation were analysed across all individuals using 10 microsatellite loci.

Results

Stypandra glauca exhibited high (chloroplast) or moderate (nuclear) levels of divergence among, and low diversity within, outcrops. Haplotype diversity was high in both sampling regions, and each haplotype was unique to one outcrop. There was little correlation between geographical and genetic distance. Both nuclear and chloroplast diversity were higher in southern (mesic) outcrops than in northern (semi-arid) outcrops, although the level of chloroplast divergence among outcrops was similar for both climatic regions.

Main conclusions

The levels of divergence and low diversity revealed in S. glauca support a scenario of prolonged isolation and persistence on granite outcrops in both mesic and semi-arid climatic regions, with no evidence of contraction–expansion dynamics across the outcrop network. The higher levels of diversity in the southern populations may result from the maintenance of a larger effective population size in southern regions, which retained more mesic climates during drier glacial periods. Although the climatic conditions differ between outcrops in this study, our results indicate that outcrops in both regions have harboured S. glauca throughout climatic changes, accentuating the value of these habitats to biodiversity conservation under future changing climate.

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